• Tweaking is changing your MTU & RWIN
settings on your PC to maximise your connection and achieve better
• MTU (Maximum
Transfer Unit) is the default packet size (amount of data) that a system
uses to send and receive information over a network.
• RWIN (Receive
Window) is the maximum amount of data that you can receive without
having to send an acknowledgement to the sender.
Changing these settings can frequently improve your connection
speeds, by decreasing the risk of fragmentation on the broadband
The History behind tweaking adsl settings.
Although it has always been possible to tweak your MTU
and RWIN settings, MTU tweaking came into its own during the period
of 2002/2003 when adsl in the UK was still in its infancy. At
that time the default MTU setting of 1500 caused processing overheads
on the exchange equipment, the effect of which was an overall deterioration
in service and speed. Therefore many users found that their connection
was not as efficient as it could have been.
In January 2003, BTw declared that the optimum MTU
setting was 1458 and made a tool available to change your settings. The
tool and more information were available from here.
Quote from BTW
Fragmentation is the
result of IP packets, larger than the 1500 byte maximum attempting
to the pass across the network. The MTU tool enables users of Microsoft
Windows based operating systems, to improve their network performance.
By modifying the MTU to a setting suitable for the network, the
MTU can be lowered to stop fragmentation, thereby improving the
perceived performance of the network. This setting is nominally
1458 bytes. The change is made to the ADSL interface whether it's
via a USB modem or an Ethernet Network Interface Card.
In July 2003 BTw undertook to carry
out work on all their exchanges to set the adsl network with
higher MTU values to stop the default windows MTU of 1500 causing
a problem. More information about this work can be found on adslguides
By this time many users were now familiar with tweaking and happy
to explore its benefits further.
The Need for Speed
By July 2003 many early adopters to adsl discovered
that although the BT network problems may have been fixed, tweaking
could bring additional benefits such as ekeing out a better speed
on your connection.
Many users on adsl-guide spent literally hours finding and trying
new settings to increase their speed.*
Various users undertook testing which did indeed prove that by
tweaking both MTU and RWIN you could improve a 512kbps by around
30kbps or more.
With the advent of (1Mb) higher speeds the same tweakers
also found that doubling your RWIN on your previous best settings
gave the optimum performance and speeds for their lines. The same
theory was recommended for 2Mb connections.
* Yes rather sadly I was
one of those that spent many a happy hour or so trying to eke
out a few extra kbps :/
Quote from me at the time "My speed (478/250kbps) increased by about
30kb after tweaking"
So where does that leave us today - with the advent
of maxdsl the increase of the extra speed is not quite so important
when talking 8Mb compared to gaining an extra 30kbps when on a
512kbps line. Some naysayers say that tweaking makes no difference.
My own opinion is that it does.... on a 2Mb connection
I get an extra 40+ kbps when tweaked against an untweaked connection.
Not that much now in the grand scheme of things - but I'm more
than happy to spend 2 mins setting my MTU and RWIN just because
I can. ;o)
Tweaking can also resolve some strange happenings
on the internet - particularly when viewing sites such as ebay
and M$ - So much so that I have devoted an MTU
I recommend that you use DrTCP for
tweaking, and Ive also written a page about How
to tweak MTU and which settings to use.
Read the next page to find out more about
to tweak and suggested settings || Understanding
MTU and RWIN || MTU Problems||
Finally, I cant complete this page without giving
due credit to the very early tweakers -
In particular Pengbo and Tam for starting me on the path to tweaking.
Also thanks to guest_again for his input in sharing his findings.
If you want an more in depth explanation try Pengbo's
website who gives a step by step guide on running Dr TCP.
More information about Dr TCP can be found at DSL
Reports and you can also use their Tweak
Test to see if your connection is optimised correctly.